1. Field of the Invention
The present invention relates to an evaluation method and control method for the imaging performance of a projection optical system, an exposure apparatus having a function which implements the methods, and a memory medium storing a computer program for implementing the methods.
2. Description of the Related Art
An exposure apparatus which projects the pattern of an original onto a substrate, thereby exposing the substrate is used in lithography for manufacturing a device such as a semiconductor device. In recent years, along with further miniaturization of device patterns, a demand for improving the resolution of the exposure apparatus is increasing.
To improve the resolution of the exposure apparatus, the NA of the projection optical system is increasing. These days, an exposure apparatus having an NA of 0.90 or more, and an immersion lithography technique of attaining an effective NA of 1.0 or more by filling the space between the substrate and the final surface of the projection optical system with a medium having a refractive index of 1.0 or more have been put to practical use.
Along with an increase in the NA, the polarization state of incident light on the projection optical system exerts a significant influence on the resolution. Under the circumstance, a technique of controlling the polarization state (the polarization state includes non-polarization in a broad sense) of the incident light has been proposed in order to attain a higher resolution.
However, in practice, optical elements (including optical elements of the projection optical system and illumination optical system, an antireflection film, a reflection film, a reticle, a pellicle, and a resist) which change the polarization state are inserted in the optical path. For this reason, an image may not be formed on the substrate with a targeted polarization state.
Examples of the factors that make the optical elements change the polarization state are the intrinsic birefringences of crystal glass materials, residual stresses imparted to an optical system material, reticle, and substrate upon manufacturing them, stress birefringences generated upon holding them, and polarization differences in the reflection/transmission characteristics of the pellicle, resist, antireflection film, and reflection film.
The polarization state of light which impinges on the object plane of the projection optical system is generally expressed by the Jones vectors or Stokes parameters. Also, a polarization change representing a change in the polarization state of incident light on the projection optical system until it exits from the projection optical system is generally expressed by the Jones matrix or Mueller matrix.
Japanese Patent Laid-Open Nos. 2006-237109 and 2006-173305 disclose techniques of evaluating the influence that the polarization state and polarization change exert on the imaging performance.
The conventional techniques are extremely inefficient because measurement or optical image simulation must be repeated a number of times in order to evaluate the imaging performance of the projection optical system and control the imaging performance of the projection optical system based on the evaluation result.